2014 年 80 巻 812 号 p. FE0088
In this study, we have developed a propulsion mechanism using a fin with variable effective length spring as variable stiffness mechanics. We measured its thrust and the lateral forces in water tank with three dimensional flow and that with quasi two dimensional environment. Additionally, three dimensional numerical analysis of the propulsion mechanism was performed. Flow field around the fin and variations of thrust and lateral forces obtained in this numerical analysis were compared with the above experimental results in the condition of rigid fin. As a result, there was a quantitative agreement between the experiments and numerical analyses. Because the computational costs of three-dimensional fluid-structure interaction analyses are very expensive, two dimensional fluid-structure interaction analyses were performed in the conditions of elastic fins. Qualitative agreement was observed between the fluid-structure interaction analyses and the above experimental results of quasi-two dimensional environment. In these conditions, an evaluated value of thrust efficiency increased with the decrease of the stiffness of the fin. The flow fields around the elastic fins were visualized to discuss the flow dynamics around the fin. From this result, it was shown that the direction of jet flow generated by vortex pair at the fin edge was closed to the rear direction of the propulsion mechanism by decreasing the stiffness of the fin.
